1. Field of the Invention
The present invention relates to a sheet processing apparatus, which receives a sheet discharged from such an image forming apparatus such as a copying machine and a printer, selectively performs a process to the received sheet, and discharged and stacks the sheet, and an image forming apparatus provided with the sheet processing apparatus.
2. Description of the Related Art
Conventionally, in the sheet processing apparatus that performs a binding process and a sorting process to the sheet in which an image is formed, the binding process and the sorting process are selectively performed on an intermediate processing tray, and the sheet (or a sheet bundle) on the intermediate processing tray is discharged and stacked on a stack tray by a discharge roller.
In the sheet processing apparatus, the sheet discharged toward the stack tray by the discharge roller falls freely and is stacked on the stack tray without guiding the sheet to a sheet stacking surface of the stack tray.
Therefore, for example, U.S. Pat. No. 6,196,542 proposes a sheet processing apparatus that performs lowering and stacking of the sheet discharged by the discharge roller toward the stack tray while guiding the sheet.
In the sheet processing apparatus disclosed in U.S. Pat. No. 6,196,542, by rotating a belt entrained about the discharge roller, a rear end of the sheet discharged by the discharge roller is lowered toward the stack tray to be stacked while supported on an elastic finger provided in a surface of the belt.
However, in some conventional sheet processing apparatuses, the discharge roller rotates normally and reversely in order to perform switchback to the sheet on the intermediate processing tray. In this case, although the finger lowered by the rotating and moving belt holds the rear end of the already-stacked sheet during the normal rotation of the discharge roller, the finger lifts the rear end of the sheet by the rotating and moving belt during the reverse rotation. Therefore, although a sheet end part can be held during the normal rotation, the rear end of the sheet stacked on the stack tray is disarrayed during the reverse rotation.